I have written some remarks in some of my works that are somewhat informal and repetitive in nature (mainly for my own clarification). I was wondering if there is a way of suppressing them when I don't want to typeset them in the PDF.

MWE:

\documentclass{article}
\usepackage{amsmath,amsthm}
\newtheorem*{remark}{Remark}
\begin{document}
\section{Inner Loop (for $l$)}
We begin with inner loop - s.t. the given constraints, we find the optimal
level for individual labour supply in equilibirum,
\begin{equation*}
l=l^{\star }.
\end{equation*}
\begin{remark}
I want to keep this remark.
\end{remark}
\begin{remark}
When necessary, I would like to typeset this remark on or off.
\end{remark}
\end{document}

Here's a minimal example that defines \ifkeepremark as a \newif and sets it to true (\keepremarktrue) or false (\keepremarkfalse) depending on whether you need it or not:

\documentclass{article}
\usepackage{amsmath}% http://ctan.org/pkg/amsmath
\newif\ifkeepremark
\begin{document}
\section{Inner Loop (for $l$)}
We begin with inner loop - s.t. the given constraints, we find the optimal
level for individual labour supply in equilibirum,
\begin{equation*}
l=l^{\star}.
\end{equation*}
\keepremarktrue
\ifkeepremark
I want to keep this remark.
\fi
\keepremarkfalse
\ifkeepremark
When necessary, I would like to typeset this remark on or off.
\fi
\end{document}

It is possible to maintain the remark environment look using the environ package. It allows for environment definition in a control sequence style:

together with the "switches" \keepremarktrue and \keepremarkfalse to selectively keep/discard remarks. The default value is \keepremarkfalse, which I've overridden with an issue of \keepremarktrue. That is, by default, allremarks will be visible.

You could also define your own remark environments based on other/alternative \newifs that you can turn on/off in the preamble (for a global modification).